Nested hollow-core anti-resonant fiber with elliptical cladding for 2 µm laser transmission

In this work, a nested hollow-core anti-resonant fiber (HC-ARF) with an elliptical cladding for high-power lasers for 2 µm laser transmission was proposed and theoretically investigated. The dual-layer elliptical tubes nested within the fiber enable the low-loss single-mode transmission. The finite element method (FEM) was employed to analyze and optimize the structure of fiber, with a total loss of less than 5 × 10^-4dB/m across the wavelength range of 1920nm to 2040nm. An extremely low loss of 1.22 × 10^-5dB/m at 1948nm was realized. A high-order mode extinction ratio (HOMER) exceeding 3 × 10⁴ was maintained across a significant bandwidth and a size tolerance ratio under 15%. Furthermore, a low loss of 5 × 10^-5dB/m at 1948nm with a bending radius over 15 cm was obtained, indicating high bending resistance. It was demonstrated that the proposed fiber has exceptional transmission performance for 2 µm laser transmission.